1. Field of the Invention
The present invention relates to a charged particle irradiation system that is used to irradiate an affected part such as a tumor with a charged particle beam so as to treat the affected part and more particularly to a charged particle irradiation system that is suitable for the correction of a beam position.
2. Description of the Related Art
There is known a charged particle irradiation system for irradiating a patient such as a cancer patient with a charged particle beam such as a proton beam. This charged particle irradiation system includes an ion beam generator, a beam transport line, and a treatment room. A charged particle beam accelerated by the ion beam generator reaches an irradiation nozzle in the treatment room through the beam transport line. The charged particle beam is then scanned by a scanning magnet included in the irradiation nozzle so that an affected part of the patient is irradiated with the charged particle beam. Heretofore, as a method used in such a charged particle irradiation system, there is known an irradiation method including the steps of: with irradiation with a charged particle beam from the ion beam generator stopped, controlling the scanning magnet so that the irradiation position of the charged particle beam is changed; and then restarting the irradiation.
Such an irradiation method is required to achieve a high degree of accuracy in position and angle of a charged particle beam. However, the position and angle of the charged particle beam from the ion beam generator may not be stable. As a solution to this, there is known a technology in which two steering magnets are disposed in a beam transport line so as to correct the trajectory of a charged particle beam (for example, refer to JP-A-2003-282300).
Moreover, there is known a technology in which beam position information acquired by a charged-particle-beam-position monitor system is used to control a scanning magnet so that a beam position is corrected (for example, refer to Published Japanese translation of PCT application No. 2002-540911).